Generally, the bicycles have been used conveniently and widely from old times as a transporting means which can run by causing the rear wheel to rotate through pedaling with the help of only legs without consumption of any fuel. Particularly recently the bicycle riding is favored by almost everyone as it is recognized as one of sports beneficial to the health in step with the rising interest in the health, because bicycles are not only free from the environment pollution owing to the exhaust gases but also the pedal movement for pressing the bicycle pedals corresponds to the aerobic exercise needed for the human body.
The ordinary bicycle, however, are somewhat too deficient in the propulsive force to be the long distance transporting means or mountaineer bicycles. Therefore, the speed change gears have been mounted on bicycles to increase the propulsive force and there has been proposed a plan to drive both the front gear and the rear gear simultaneously. However, such bicycles mostly failed to be put to practical use because of the unreliable operation and considerable resistance in the power transmitting processes.